US2924556A - Heat processing of fine-granular coal products - Google Patents

Description

I HEAT-PROCESSING OF FINE-GRANULAR COAL PRODUCTS Filed Oct. 14, 1955 HEAT PROCESSING OF FlNE-GRANULAR COAL PRODUCTS Alfred Jaeppelt, Dortmund, Otto Diettrich, Koln-Braunsfeld, and Othmar Werner, Koln-Bayenthal, Germany Application October 14, 1955, Serial No. 540,497 Claims priority, application Germany October 14, 1954 13 Claims. (Cl. 202-22) Our invention relates to the heat processing of finegranular fuel, such as coal dust for use in dust burning or gas producing equipment.

The heating of fine-granular, non-caking fuels in suspension within hot gases, as compared with the indirect heating of thin layers of coal, has the advantage of requiring less time due to the rapid heat transfer from the hot gases into the suspended coal granules. For instance, when drying brown coal (German ligintic coal) a high continuous throughput is applicable, even with a water content of the coal above 50%; and a heat treating period of less than one minute is suflicient.

Attempts have therefore been made to apply this method also for the purpose of heating ncn-caking finegranular fuel to such higher temperatures as are required for carbonizing or coking the fuel. It has been found, however, that under such conditions they rate of temperature increase is no longer as favorable as when heating the fuel to the lower drying temperatures at which a large temperture gradient is effective between the heat-carrier gas and the solid coal granules. Another disadvantage of thus carbonizing or coking the solid fuel in suspension within a gas of the same flow direction is the fact that, on account of the high waste-gas temperature, the operation is economically unfavorable.

It is an object of our invention, therefore, to provide a continuous heat-processing method for the carbonization or coking of fine-granular fuel that affords basically the advantages of heating in gaseous suspension but eliminates the above-mentioned disadvantages.

More particularly, it is an object of the invention to provide a continuous heat processing of pulverulent coal products at carbonizing temperature that is suitable to secure the large throughput required for industrial application while also affording an improved heat economy and overall efliciency as compared with the processes heretofore available for such purposes.

To this end, and in accordance with our invention, we heat the granular fuel in a sequence of heating steps that are consecutively graduated from lower to higher temperatures respectively and that occur within respective heat exchangers of the cyclone type serially traversed by a single, continuous flow of hot gases; and we introduce the fuel material, suspended in the gas flow and conveyed thereby in the gas-flow direction, into a heat exchanger near a point of the gas flow of relatively low temperature, and we then pass the fuel material, separated in the heat exchanger, back into the same gas flow but at a point of higher temperature located, relative to the gas flow, ahead of the next-preceding heat exchanger, and so forth.

More specifically, we introduce the fuel material into the gas conduit that connects the serially last cyclone with the cyclone next preceding in the gas path. After separation of the fuel material from the heating gas in the last cyclone, we pass the fuel material through a sealing and dosagemetering device into the gas conduit leading into the next preceding cyclone, and coming from the gas outlet of the second-preceding cyclone. The

2,924,556 Patented Feb. 9, 1960 number of cyclones serially connected by gas conduits depends upon the desired degree of heating to be imparted to the fuel.

The fine-granular non-caking coal to be processed is to be introduced into the above-described heating sequence in relatively dry condition. For the processing of fuel having a higher humidity content than desired in the carbonizing process, and in accordance with another feature of our invention, we first subject the granular fuel to drying or preheating before introducing it into the main cyclone system. The pre-heating is effected also by means of hot gases in which the granules are suspended and conveyed in the flow direction of the gases, substantially in the konwn manner; but we join the preheating operation with the main heating or carbonizing operation by employing a cyclone-type heat exchanger in the pre-heating step and connecting the dust outlet of this cyclone directly with the inlet through which the fuel material is introduced into the main heating sequence.

When thus processing fuel material of high water content, it is preferable to discharge the spent heating gases of the pre-heating or drying operation separately from the flow of gases in the main heating or carbonizing sequence. This prevents dilution of the tar-containing gas in the main heating sequence by the scavenging gases resulting from the pre-heating operation and containing an admixture of large amounts of steam. Besides, the waste gases of the main sequence are combustible, and hence can be utilized as fire gases in the required furnace or for other heating purposes.

The pre-heating operation and the main heating operation can be carried out under nearly equal static pressures. It is preferable, however, to conduct the preheating operation under low or negative pressure, for instance mm. water column, and the main heating under super-atmospheric pressure, for instance 400 mm. water column. The pressure loss in the heating operation is dependent upon the number of the cyclones, the amount of fuel throughout, and the temperature gradient of the scavenging or heating gases. The heating gases in the pre-heating operation may contain oxygen, whereas oxygen-free gas must be used in the main heating or carbonizing operation. The pre-heating operation need not be used when the fuel material to be processed is poor in water.

The operations and flow of substances occurring in a process according to the invention are further apparent from the schematic diagram shown on the drawing.

A combustion furnace 1 is supplied with generator gas or blast-furnace top gas at In, and with air at 1b. The gases of combustion are exhausted by means of a blower 2 and pass from furnace 1 through a pipe 10 and a preheater pipe 3 into a cyclone 6 and thence through the top outlet of the cyclone and a pipe 6a into the blower 2. A small portion of the gases, used for preheating the fuel, is applied for regulating the preheater-gas temperature by passing it through a pipe 2a back into the preheater pipe 3. The temperature of the mixed gases at the entrance of the pre-heater pipe is thus kept between about 700 to 1100 C., depending upon the water content of the fuel to be dried. The remaining major portion of the preheater gases is discharged at 7 into the open atmosphere through a quantity-regulating member (not shown). The fuel to be processed, for instance lignite (German brown coal) with a water content of about 50%, is supplied in granular form, preferably of a grain size below 10 mm, from a bin or hopper 4 through a rotating cell wheel 5 into the preheater pipe 3. The cell wheel 5 serves as a seal to prevent the escape of gas and it also controls the supply of granular fuel mass in accordance with the desired volumetric quantity.

The granules are entrained by the gas flow in pipe 3 and are conveyed in suspension to pass in the gas-flow direction toward the cyclone while being dried by the hot gases entering through pipes and 2a. After drying, the fuel may retain a water content of up to 4%, for in stance. In cyclone 6 the preheated and dried fuel material is separated by centrifugal action at a temperature of 100 to 150 C., and is then sluiced out by means of a cell wheel 8.

Thence the fuel material enters through a pipe 8a directly into a gas conduit 10a of the main heater portion of the processing equipment and passes sequentially through the cyclones 9, 10, 11 and 12. Each of these cyclones is equipped with a gas sealing, dosage-metering and discharging device designed, for instance, as a cell wheel 13, 14, and 16 respectively. The heating gases required for the main heater portion, according to the schematic diagram, are produced as gases of combustion in a furnace 17. It is supplied at 17a with generator or top gas and at 17b with air. The gases of combustion pass from furnace 17 sequentially through a conduit 170 into cyclone 12, from the gas outlet of cyclone 12 through a conduit 12a into cyclone 11, thence through a conduit 11a into cyclone 10, through another conduit 10a into cyclone 9, and through a conduit 18 into a condenser 19 from which the spent gases are discharged at 19a.

The preheated fuel material, entering into the main heater portion of the system through pipe 8a, is entrained by the hot scavenging gas passing through conduit 1% from cyclone 10 into cyclone 9. A direct heat exchange occurs in conduit 10a between the scavenging gas and the dried fine-granular fuel. This heat exchange is continued within the cyclone 9 to a particularly effective degree. Thereafter, the fuel is discharged through the cell wheel 13 and passes through discharge pipe 13a into gas conduit 11a. The hot gas passing from cyclone 11 through the conduit 11a now conveys the fuel into cyclone 10. In conduit 11a and, to a major degree within cyclone 10, a second direct heat exchange at a higher temperature occurs between the hot gases and the fuel material. The fuel separated in cyclone 10 then passes through dust discharge pipe 14a, while the scavenging gas passes through conduit 10a from the top outlet of cyclone 1t) to cyclone 9.

In conduit 1211, the fine-granular fuel now admixes itself with the scavenging gas coming from cyclone 12 and is thus conveyed into cyclone 11. In conduit 12a, and pmticularly in cyclone 11, the fuel is subjected to another stage of heating treatment at a still higher temperature Subsequently, the gas passes out of cyclone 11 through conduit 1111 into cyclone 10, while the heated fuel granules are discharged through cell wheel 15 and dust discharge pipe 15a. The discharged fuel, admixed with the hot gases that pass from the combustion furnace 17 through conduit 170, now is conveyed into cyclone 12. After the material is again heated, it is discharged at a temperature of 300 to 900 C. through cell wheel The above-mentioned final temperature of the fuel material depends upon the properties of the fuel being treated, particularly upon the desired residual content of volatile components. For instance, at a final temperature of the processed fuel material of about 400 C., the residual amount of volatile components may amount to 28 to 32% when processing fine-granular brown coal (German lignite). The material discharging from pipe 16a can be cooled in the known manner if desired, for instance, by slaking with water.

The hot scavenging gas coming from the combustion furnace 17 at a temperature of 400m 1100 C., imparting its heat to the granular fuel material sequentially in cyclones 12, 11, 10 and 9, becomes increasingly laden with tar mist before it passes through conduit 18 at a temperature of 150 to 300 C. into the condenser 19. The lower temperature limit of 150 C. is applicable if a partial condensation of the tar mist is desired prior to the exit gases entering into the condenser 19. The upper temperature limit of 300 C." must not be exceeded for heat-economical reasons.

The gas conduit leading into the combustion furnace 17 at 17a and 17b are preferably each equipped with a blower, so that the combustible gas as well as the air of combustion are introduced in the furnace 17 and thus also into the heater portion of the plant under slight super-atmospheric pressure.

The cyclones 6, 9, 10, 11 and 12 are in accordance with the designs conventionally used for separating dust from air or gas; that is, they operate on the principle of centrifugal separation.

The hot scavenging gases required in the preheater and main heater portions may also be produced in a single combustion furnace, since the temperature of the gases entering into the preheater portion can be controlled by the return of a cooler amount of these gases.

As a rule, the duration of the preheating or drying operation in the preheater portion is about 20v to 60 seconds, and the fuel material may be passed through the main heater portion within a period of 20 seconds to 2 minutes, for instance.

The heat-processed fuel material obtained in the abovedescribed manner can be used, for instance, for the operation of coal-dust burners or for the purpose of gas production. The process is particularly advantageous in permitting a high throughput at a particularly favorable heat economy.

In order to prevent the condensation of tar mists in the main heating portion and the precipitation of tar onto the coal granules, and also for obtaining a largest possible yield in tar, the exit gas temperature of the main heating portion is to be kept above the dew point of the tar within the gas. This is done by suitably controlling the temperature or quantity or both magnitudes of the gas supply. The danger that tar mists may con-. dense onto the coal to be heated is very slight when the preheating step is combined with the main heating sequence, that is when the process is applied to the heating of fuels of high water contents. This is so because the fine-granular fuel is directly sluiced from the preheater portion into the main heater portion so that no appreciable heat losses are involved. However, if it is desired to obtain a tar of greatest possible degree of cracking, for instance when carbonizing fuels whose tar is of inferior. quality, then it may be favorableto operate so that the exit temperature of the scavenging gases leaving the main heating portion is below the dew point of the tar vapors in order to cause a condensation of the heavy components or the precipitation of these components onto the preheated coal. The tar thus condensed and precipitated is then re-distilled in the main heating portion.

The heat processing method, according to the inven-.

tion, is particularly advantageous for the coking of mixtures composed of non-caking and caking fuels, such as non-caking and caking bituminous coal. The non-caking componentof such mixtures may consist of low-volatile or high-volatile bituminous coal such as German Steinkohle of the non-caking variety, lignite such as brown coal of German origin, or peat. The caking component may consist of low-volatile or high-volatile bituminous coal such as German Steinkohle? of the lean variety. For the production of a good mixed coke from such materials, it is necessary to mix the non-baking fuel in deg asified condition with the baking fuel prior to coking the mixture. It is preferable to adapt the non-caking coal to this use by aspecific or predetermined degree of degasification, this being dependent upon the caking qualities of the caking coal to be admixed. Such an adaptation of the gas contents of the non-baking coal is possible in a particularly simple manner by applying the heating method according. to the invention. For

instance, it has been found. particularly advantageous if the heating of non-caking fuel. material in the main heater portion is so carried out that'a residual content of volatile components in an amount of 20 to 25% is obtained. When the resulting material is mixed in a proportion of 1:1 with a good caking coal having a content of dry volatile matter of about 30% for instance,

the mixture, upon coking in a coke furnace, produces a metallurgical coke of good quality; that is, a coke .material suitable for the smelting of iron ore in blast furnaces.

We claim:

1. The method of carbonizing non-caking fine-granular coal in suspension within heating gases and in continuous operation, which comprises the steps of passing a flow of hot substantially oxygen-free combustion gases serially through a number of cyclones so that said cyclones have decreasing temperatures respectively from the serially first to the last cyclone, charging dry granular coal into the hot combustion gas flow entering the last cyclone whereby the coal is heated and separated from the gas in said last cyclone, passing the coal separated from the gas and still in heated condition from each cyclone, excepting the first one, into the hot combustion gas flow entering the next preceding cyclone, the gas being hotter than the coal, whereby the coal is heated to a higher temperature and again separated from the gas flow, adjusting the volumetric quantity of the gas flow entering the first cyclone as required to maintain the exit temperature of the tar-laden gases at the last cyclone above the dew point of the tar vapors entering into the gas due to carbonization of the coal, and discharging the carbonized coal from the first cyclone of the gas-flow series, the coal being carried in suspension co-currently by the hot combustion gases flowing to the cyclones.

2. The method of heating coal comprising suspending the coal in fine granular form in a current of hot gases, passing the coal and gases co-currently through a zone in which the gas pre-heats the suspended coal and thence co-currently into a cyclone separator in which further heat exchange between the gases and the coal takes place, removing the coal separated from the gas in the said separator and passing the separated coal in co-current suspension in a current of gases hotter than the first into a second cyclone separator in which the coal is heated to a higher temperature than in the first cyclone separator.

3. The method of drying and heating coal comprising suspending the coal in fine granular form in a current of hot gases, passing the coal and gases co-currently upwardly through an elongated zone in which the gas preheats the suspended coal and thence co-currently into a cyclonic separation zone in which further heat exchange between the gases and the coal takes place to dry the latter, removing the coal separated from the gas in the said separation zone and passing the separated coal in co-current suspension in a current of gases hotter than in the first cyclonic zone and hotter than said separated coal, into a second cyclonic separation zone in which the coal is heated to a higher temperature than in the first cyclonic separation.

4. The method of carbonizing coal comprising suspending the coal in fine granular form in a current of hot gases, passing the coal and gases co-currently through a zone in which the gas pre-heats the suspended coal and thence co-currently into a cyclone separator in which further heat exchange between the gases and the coal 'takes place, removing the coal separated from the gas in the said separator and passing the separated coal in co-current suspension in a current of oxygen-free combustion gases hotter than the first gases into a second cyclone separator in which the coal is heated to a higher temperature than in the first cyclone separator.

5. A continuous process for heating fine granular noncaking coal in suspension in hot gas in at least three stages .6 including a cyclonic heating and separation in each stage, the coal being progressively heated up from the first to the third" stage, comprising passing the granular coal in a stream of hot gas to' a third stage cyclonic heat- 1 granular coal into said hot gases and passing these gases and coal into the first stage cyclonic heating and separation.

6. The process of claim 5 in which the said heating is at a temperature sufiiciently high to at least partially carbonize the coal.

7. The process of claim 5 in which the hot gases are combustion gases substantially free of oxygen and are at carbonizing temperature in at least the third stage cyclonic heating.

8. The method of carbonizing non-caking fine-granular coal in suspension within heating gases and in continuous operation in several heating-up stages, which comprises the steps of passing a flow of hot combustion gases serially through a plurality of cyclonic coal heating-up zones at an exit temperature between about C. and about 300 C. at the last cyclonic zone, charging dry granular non-caking coal into the gas flowing into the serially last cyclonic zone, passing the cyclone-heated coal, separated from the cyclone separated gas, from each cyclonic zone, excepting the first one, into the gas flow entering the next preceding cyclonic zone, which entering gas is hotter than the coal, and discharging the carbonized coal from the first cyclonic zone of the gas-flow series, the coal being carried in suspension co-currently by the hot combustion gases flowing to the cyclonic zones.

9. The method of carbonizing non-caking fine-granular coal in suspension within heating gases and in continuous operation in several heating-up stages, which comprises the steps of pre-heating moist granular coal in gaseous suspension and separating the dry coal from the moisture-laden gas, passing a flow of hot combustion gases substantially oxygen-free serially through a plurality of cyclonic coal heating-up zones at an exit temperature between about 150 C. and about 300 C. at the last cyclonic zone, charging the pre-heated coal when still in heated condition into the gas flow entering the serially last cyclonic zone having the lowest temperature of said plurality of cyclonic zones, passing the cycloneheated coal, separated from the cyclone separated gas, from each cyclonic zone, excepting the first one, into the gas flow entering the next preceding cyclonic zone, having a higher temperature, and discharging the carbonized coal from the first cyclonic zone of the gas-flow series, the coal being carried in suspension co-currently by the hot combustion gases flowing to the cyclones.

10. The method of making coke material suitable for smelting iron ore in blast furnaces, comprising carbonizing non-caking fine-granular coal in suspension within heating gases and a continuous operation in several heating-up stages, by the steps of passing a flow of hot combustion gases serially through a plurality of cyclonic coal heating-up zones at an exit temperature between about 150 C. and about 300 C. at the last cyclonic zone, charging dry granular coal into the gas flowing into the serially last cyclonic zone, passing the cyclone-heated coal, separated from the cyclone separated gas, from each cyclonic zone, excepting the first one, into the gas flow entering the next preceding cyclonic zone, which entering gas is hotter than the coal, and discharging the carbonized coal from the first cyclonic zone of the gas-flow series,

said heating .being carried out so that a carbonized prodv not having a residual content of volatile components of about 20 to 25% results, and mixing the product with a good caking coal and coking the mixture.

11. The method of removing volatiles from coal by direct contact with hot gases, comprising suspending the coal in fine granular form in a current of hot carrier gases, passing the coal and gases cocurrently through a zone in which the gas directly pre-heats the suspended coal and thence co-currently into a cyclone separator in which further direct heat exchange between the gases and the coal takes place, removing the coal separated from the gas in the said separator and passing the separated coal in co-current suspension, in a current of gases hotter than the first and which entering gas is hotter than the coal, into a second cyclone separator in which the coal is directly heated by said hotter gases to a higher temperature than in the first cyclone separator.

12. A continuous process for carbonizing fine granular non-caking coal in suspension in hot non-oxidizing combustion gas in at least three stages including a cyclonic heating and separation in each stage, the coal being progressively heated up from the first to the third stage by the hotter entrant gases to each stage, comprising passing the granular coal in a stream ofsaid hot gas to the third stage cyclonic heating and separation, removing the hot gases separated from the third stage, removing granular coal separated in the first stage cyclonic heating and separation and conveying it in the hot gases separated from the third cyclone stage into a second stage cyclonic heating and separation, removing the granular coal separated in the second cyclonic stage and passing it in said first-mentioned stream of hot gases to the third stage cyclonic heating and separation as aforesaid, removing the hot gases separated from the second cyclonic heating stage and introducing granular coal into said hot gases, the entrant gases being hotter than the coal, and passing these gases and coal into the first stage cyclonic heating and separation, the exit gases from the first stage heating being at about 150 to 300 C., the inlet gases to the third stage heating being at about 400 to 1100 C.

13. A continuous process for carbonizing fine granular pre-heated and at least partly dried non-caking coal in suspension in hot non-oxidizing combustion gas in at least three stages including a cyclonic heating and separation in each stage, the coal being progressively heated up from the first to the third stage, comprising passing the granular coal'in a stream of said hot gas to the third stage cyclonic heating and separation, removing the hot gases separated from the third stage, removing granular coal separated in the first stage cyclonic heating and separation and conveying it in the hot gases separated from the third cyclone stage into a second stage cyclonic heating and separation, removing the granular coal separated in the second cyclonic stage and passing it in said firstmentioned stream of hot gases to the third stage cyclonic heating and separation as aforesaid, removing the hot gases separated from the second cyclonic stage and introducing pre-heated and partly dried granular coal into said hot gases and passing these gases and the coal into the first stage cyclonic heating and separation, the exit gases from the first stage heating being at about to 300 C., the inlet gases to the third stage heating being at about 400 to 1100 C., the pre-heating of the coal being carried out by suspending the granular coal in hot gases and causing the suspension to whirl about in a cyclonic zone, separating the coal from the gas in said zone and introducing said coal into the first stage cyclonic heating and separation, as recited.

References Cited in the file of this patent UNITED STATES PATENTS Re. 17,181 McEwen Ian. 1, 1929 2,085,903 Fitz July 6, 1937 2,512,076 Singh June 20, 1950 2,534,051 Nelson Dec. 12, 1950 2,623,011 Wells Dec. 23, 1952 2,654,699 Lesher Oct. 6, 1953 2,706,706 Pettyjohn Apr. 14, 1955 2,719,112 Kearby et al. Sept. 27, 1955 2,734,853 Smith et al Feb. 14, 1956 2,735,804 Boston et al. Feb. 21, 1956 2,751,334 Scott June 19, 1956 FOREIGN PATENTS 670,882 Germany Jan. 27, 1939 501,374 Great Britain Feb. 27, 1939 OTHER REFERENCES Sohns et al.: Industrial and Engineering Chemistry, page 461, March 1955.

Claims (1)

1. THE METHOD OF CARBONIZING NON-CAKING FINE-GRANULAR COAL IN SUSPENSION WITHIN HEATING GASES AND IN CONTINUOUS OPERATION, WHICH COMPRISES THE STEPS OF PASSING A FLOW OF HOT SUBSTANTIALLY OXYGEN-FREE COMBUSTION GASES SERIALLY THROUGH A NUMBER OF CYCLONES SO THEAT SAID CYCLONES HAVE DECREASING TEMPERATURES RESPECTIVELY FROM THE SERIALLY FIRST TO THE LAST CYCLONE, CHARGING DRY GRANULAR COAL INTO THE HOT COMBUSTION GAS FLOW ENTERING THE LAST CYCLONE WHEREBY THE COAL IS HEATED AND SEPARATED FROM THE GAS IN SAID LAST CYCLONE, PASSING THE COAL SEPARATED FROM THE GAS AND STILL IN HEATED CONDITION FROM EACH CYCLONE, EXCEPTING THE FIRST ONE, INTO THE HOT COMBUSTION GAS FLOW ENTERING THE NEXT PRECEDING CYCLONE, THE GAS BEING HOTTER THAN THE COAL, WHEREBY THE COAL IS HEATED TO A HIGHER TEMPERATURE AND AGAIN SEPARATED FROM THE GAS FLOW, ADJUSTING THE VOLUMETRIC QUANTITY OF THE GAS FLOW ENTERING THE FIRST CYCLONE AS REQURED TO MAINTAIN THE EXIT TEMPERATURE OF THE TAR LADEN GASES AT THE LAST CYCLONE ABOVE THE DEW POINT OF THE TAR VAPORS ENTERING INTO THE GAS DUE TO CARBONIZATION OF THE COAL, AND DISCHARGING THE CARBONIZED COAL FROM THE FIRST CYCLONE OF THE GAS-FLOW SERIES, THE COAL BEING CARRIED IN SUSPENSION CO-CURRENTLY BY THE HOT COMBUSTION GASES FLOWING TO THE CYCLONES.

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